Transverse myelitis is a rare neurological condition. It's caused by inflammation (swelling) of the spinal cord. The swelling damages the nerves and can leave permanent scars or lesions. The scars or lesions interrupt the communication between the nerves in the spinal cord and the rest of the body. 'Transverse' refers to the swelling being across the width of the spinal cord. It's also sometimes used to describe swelling that only affects part of the width of the spinal cord.